In the majority of patients with dilated cardiomyopathy the etiology is unknown. Many patients with dilated cardiomyopathy complain of anginal-type pain despite angiographically normal epicardial coronary arteries. To examine whether abnormalities in coronary flow exist in dilated cardiomyopathy, 26 patients with dilated cardiomyopathy and normal epicardial coronary arteries, 12 of whom had frequent chest pain by history, underwent measurement of great cardiac vein flow and myocardial metabolism at rest and during pacing to a heart rate of 150. During pacing following administration of ergonovine, all 12 patients with a history of chest pain experienced their typical pain. Compared to patients without chest pain, their coronary flow was lower and coronary resistance higher, with increased myocardial oxygen extraction suggestive of myocardial ischemia. Additionally, there was a greater increase in left ventricular filling pressures in this group. There was no significant change in EKG or epicardial coronary luminal diameter by angiography. Administration of dipyridamole 0.5 to 0.75 mg intravenously to 20 patients demonstrated that those 7 patients with a history of angina pectoris also had impairment in transmural coronary flow reserve compared to the 13 patients without chest pain. Thus, patients with dilated cardiomyopathy and chest pain by history may have limited coronary vasodilator reserve, especially after vasoconstrictor stimulus. Whether this contributes to myocardial damage in dilated cardiomyopathy or is an epiphenomenon of an unrelated etiology, remains to be determined.